Combined Wide-Narrow Double Modulation of Spin-Torque Oscillators for Improved Linewidth During Communication

Spin-torque oscillators (STOs) offer the advantage of high modulation rates. However the existence of regions with high-frequency nonlinearity, accompanied by increased signal linewidth, limits both the usable STO frequency range and the minimum frequency of modulation. On the other hand, use of a large modulation frequency increases the frequency modulation (FM) bandwidth. In order to overcome these problems, we propose to simultaneously modulate the STO with two signals having different frequencies. We use a high-frequency, “wide” (f_W=500 MHz), modulation signal to improve the STO linewidth. At the same time we use a low-frequency, “narrow” (f_N=40 MHz), modulation signal to show successful narrow bandwidth modulation of the improved STO signal. The proposed method of combined wide-narrow double modulation can significantly improve the usable operating frequency range of the STOs for communication applications.